The present invention relates to a film forming apparatus for use in a semiconductor manufacturing process, and in particular, to an apparatus for forming films, a method of fabricating a semiconductor in a semiconductor manufacturing process of forming a film of silicon oxide, a film of silicon nitride, and a coating film primarily including carbon.
Description of the Prior Art
Recent development of integration of large-scale integrated semiconductor circuits has resulted in a complex wiring structure to establish connections between the respective constituent elements of the semiconductor circuits.
To prevent wires from intersecting each other, when there is formed a detour for wires, an area occupied by the wiring is increased in relation to a chip area. Furthermore, the total length of wiring becomes longer, which leads to a problem of signal transmission delay through the wire regions.
In consequence, it is generally employed a technology, called "multi-layer wiring" in which an insulation film or layer is inserted between wiring layers to form a multi-layer wiring structure to thereby prevent intersections between wiring layers.
In the multi-layer wiring technology, it is essential to minimize capacity between wiring regions in each layer and capacity between vertically arranged wiring layers. In other words, the increase in the capacity between wiring layers causes a signal transfer delay through the wiring regions. When a signal containing a high-frequency component is propagated through two wiring regions vertically disposed with an insulating film therebetween, there possibly occurs a phenomenon of crosstalk between the wiring regions, which leads to a wrong operation.
In consideration of the technological background described above, there has been discussed a technology to employ as an insulation thin film between layers a film having a small value of specific inductive capacity .epsilon. r in place of such materials of insulation films broadly utilized in the large scale integration (LSI) technology as Si.sub.3 N.sub.4 (.epsilon. r is about 7) and SiO.sub.2 (.epsilon. r is about 3.9). Attention has been directed to a film of amorphous carbon fluoride as such a substance.
For example, in accordance with the Japanese Patent Application Serial No. 08-321694, an amorphous carbon fluoride is used as a material having a low specific inductive capacity.
Since the carbon-fluoride film is easily etched by an oxygen gas in a plasma state, it is impossible to fabricate an ordinary through-hole using resist. Consequently, in the article above, a film of silicon oxide or nitride is formed at least on an upper surface of the film of amorphous carbon fluoride to manufacture a laminated structure of "silicon-oxide layer/carbon-fluoride layer/silicon-oxide layer" or "silicon-oxide layer/carbon-fluoride layer/silicon-nitride layer". The silicon-oxide layer or the silicon-nitride layer is adopted as a cover film against the oxygen plasma gas as well as a smoothening or flattening insulation film in a chemical machine polishing (CMP) process.
Referring now to FIG. 8, description will be given of an outline of the method of fabricating a semiconductor device using a carbon-compound film.
First, a carbon-compound film 802 is accumulated between wiring metal regions 801. This process is achieved through chemical-vapor deposition (CVD) with a gas of carbon fluoride such as C.sub.4 F.sub.8. In this operation, a bias power of several tens of watts is applied to a substrate to grow a film of amorphous carbon fluoride between fine wiring regions or layers.
Additionally, between a base silicon substrate 803 and the carbon layer 801 and between the wiring metal region 802 and the carbon layer 801, there is accumulated a film of silicon oxide including excessive amount of silicon in its composition. This increases the fixing force therebetween, namely, these regions are tightly fixed onto each other.
Next, a film of silicon oxide 804 is accumulated on the carbon layer 802. Also in this process, a film of silicon oxide including excessive amount of silicon in its composition is grown between the carbon layer and the film of silicon oxide to increase the fixing force therebetween.
Subsequently, the film of silicon oxide is subjected to a chemical mechanical polishing process to smooth an upper surface thereof. Furthermore, the film of silicon oxide and the carbon-compound film are etched by the known lithography to accumulate a known plug metal 805 such as aluminum in holes 807 thus opened. Thereafter, a second-layer metal 806 is accumulated thereon to resultantly form a multi-layer wiring structure.
It can be naturally considered that more than two layers of wiring are fabricated by repeatedly conducting the process described above.
FIG. 6 shows a general example of a film forming apparatus to fabricate a film of amorphous carbon fluoride and a film of silicon oxide.
The configuration of this apparatus includes a sample holder 607 also serving as a lower electrode and a silicon wafer 606 placed thereon. In this regard, when a material other than silicon exists at least on a portion of its surface, the item is called a silicon wafer so as to be discriminated from a silicon substrate. In this specific example, an electrostatic chuck is employed as the sample holder 607.
In general, a gas of helium is ejected onto a rear surface of the silicon wafer 606 from the sample holder 607 cooled by a water-cooling machine to increase the thermal conductivity of the substrate. Consequently, heat of the substrate is imparted to the sample holder 607, which resultantly cools the substrate.
In the structure, there is provided a high-frequency bias power source 608 to apply a high-frequency power to the sample holder 607 independently of the plasma source.
By applying a high-frequency wave to the sample holder 607, it is possible to effectively apply a negative bias to the silicon wafer 606. Namely, the ion energy can be controlled, for example, to improve the characteristic of embedding.
In the conventional apparatus shown in FIG. 6, since the plasma is generated by a Helicon wave. Specifically, a high-frequency wave is introduced from a high-frequency power source 601 onto an antenna 603 arranged on an outer circumference of a quartz chamber 602 to efficiently generate magnetic fields of a permanent magnet 605 and an electromagnet 609, which are also arranged on an outer circumference of a quartz chamber 602, so as to generate plasma in the chamber 602.
It is natural to be appreciated that the discharging process to form the carbon-compound film and/or the film of silicon oxide is not limited to the Helicon wave process. Heretofore, there have been already employed the electron cyclotron resonance, the inductive coupling, and the capacity coupling for the discharge process.
In addition, for example, as described in the Japanese Patent Laid-Open Serial No. 4-368119, there has been proposed a technology of forming films of a semiconductor device in which members existing in the neighborhood of a substrate to be processed are rough finished to have coarse surfaces. This prevents a coating film and the like fixed onto the members from peeling off therefrom. However, there has been no discussion about the problem related to thermal decomposition of the film of amorphous carbon fluoride.
The Japanese Patent Laid-Open Serial No. 6-208959 describes a method of manufacturing a semiconductor device in which a wolfram film is formed by chemical vapor deposition. However, there has not been any discussion about a technology using a film of amorphous carbon fluoride.
In accordance with the conventional technology, generally, in an apparatus to form a thin film of carbon compound, a film of silicon oxide, a film of nitride, and the like, when a holder of an electrostatic chuck type is adopted as the sample holder 607, the holder is restrictively required to have a diameter smaller than that of the silicon wafer 606 in any case because of the following reasons.
That is, in a case in which the employed sample holder 607 of the electrostatic chuck type has a diameter larger than that of the silicon wafer 606, when the film forming process is repeatedly accomplished, the thickness of the film accumulated on the pertinent member becomes greater. This leads to a problem of difficulty in the fixing of the silicon wafer 606 and reduction in the substrate cooling efficiency.
Additionally, there exists a problem of increase in the surface temperature of the sample holder 607 in an area thereof which is exposed to the high-density plasma, and hence the holder 607 is deteriorated.
On the other hand, when the employed sample holder 607 has a diameter smaller than that of the silicon wafer 606, any surface of the holder 607 is not exposed to the high-density plasma and hence the problem above is not to be considered.
However, if the sample holder 607 cannot be brought into contact with the periphery of the silicon waver 606, there arises a problem of decrease in the cooling efficiency of the outer-most periphery of the wafer 606.
When a laminated structure of a combination of "silicon-oxide layer/carbon layer/silicon-oxide layer" or "silicon-oxide layer/carbon layer/silicon-nitride layer" is produced by use of a sample holder described above, a film of silicon nitride or an oxide is ordinarily accumulated and then a carbon-compound layer is formed with the substrate temperature set to about 100.degree. C.
For the carbon film, since the substrate bias is 50 watts (W) or less to improve the embedding characteristic, the temperature of the periphery not cooled is increased at most about 120.degree. C. The film is accumulated on the overall surface of the wafer 606.
Subsequently, a film of silicon nitride or oxide is accumulated on the carbon-compound film. To improve the quality of the accumulated film and the embedding characteristic in the process, when there is adopted a high-density plasma and the substrate temperature is increased up to about 300.degree. C. by a bias power of about one kilowatt (Kw) in the film forming process, the peripheral portion of the wafer 606 is heated to a temperature of more than about 400.degree. C. which the film of amorphous carbon fluoride can withstand.
This resultantly leads to a problem that the film of amorphous carbon fluoride is decomposed and generates gas and hence the film of silicon oxide peels off.